Blade constructed of composite materials, having a structural core and a covering of profiled cladding, and process for manufacturing the same

Abstract

Helicopter rotor blade constructed of composite materials has a structural core (1) and a covering of profiled cladding (8). The structural core (1) includes all the structural elements of the blade, while the covering of the cladding (8) is a non-stress-bearing covering comprising an external rigid and thin shell (9a-9b), with the desired aerodynamic porfile, and a layer (10a-10b) of a ligth and flexible comformable non-stress-bearing material, such as a foam, ensuring the filling between the structural core (1) and the external shell (9a-9b). The foam layer (10a-10b) absorbs and compensates for the differences in shape between the contour of the structural core (1) and the precise aerodynamic profile of the non-stress-bearing external shell (9a-9b). The blade covering is expendable and evolutive spanwise as well as chordwise, with an external shell exhibiting an excellent surface condition, good erosion behavior and impact resistance, and easy to repair.

I claim: 
     
       1. Blade made of composite materials and having an aerodynamic profiled section, said blade comprising (a) a stress-bearing core, constituted by a resistant structure for providing alone the overall mechanical behavior of the blade, mainly against tensile efforts produced by centrifugal forces, bending moments due to flapping and drag movements of the blade, and torsional moments about a longitudinal axis of the blade, said core having an external contour which is contained with spacing within said aerodynamic profiled section,   (b) an aerodynamic conformation covering, surrounding said stress-bearing core without participating in overall structural resistance of said blade, said covering comprising (i) a thin rigid external shell having a cross-section defining said aerodynamic profiled section; and   (ii) an internal filling and conformable layer made of a light flexible non-stress bearing deformable material which fills said spacing between said core external contour and said covering external shell and connects said stress-bearing core to said covering external shell.     
     
     
       2. The blade as claimed in claim 1, wherein said core (1) comprises (a) at least one spar constructed of rovings of fibers having a high mechanical resistance which are agglomerated by a polymerized synthetic resin;   (b) an internal stress-bearing, rigid shell, participating in the structural resistance of the blade and comprising at least one layer of fabric of fibers having a high mechanical resistance which are agglomerated by a polymerized synthetic resin; and   (c) at least one filling element made of a light synthetic material disposed within said stress-bearing shell;   (d) wherein said stress-bearing shell, said at least one spar and said at least one filling element are assembled so as to constitute said structural core.   
     
     
       3. The blade claimed in claim 1 or 2, wherein said thin, rigid shell of said aerodynamic conformation covering is made of a layer of thermo plastic resin. 
     
     
       4. The blade claimed in claim 3, wherein said thermoplastic resin of said external shell is dyed in the mass. 
     
     
       5. The blade claimed in claim 3, wherein said thermoplastic resin of said external shell is painted. 
     
     
       6. The blade claimed in claim 3, wherein said thermoplastic resin of said external shell is reinforced with fibers selected from a group consisting of inorganic and organic fibers. 
     
     
       7. The blade claimed in claim 1 or 2, wherein said thin, rigid external shell of said aerodynamic conformation covering comprises at least one anti-erosion layer made of fabric of fibers selected from a group consisting of organic and organic fibers which are agglomerated by a polymerized synthetic resin. 
     
     
       8. The blade claimed in claim 1 or 2, wherein said filling and conformation layer is made of a material selected from a group consisting of cellular material and flexible foam. 
     
     
       9. The blade claimed in claim 1 or 2, wherein said aerodynamic conformation covering consists of two laminated and complementary parts, which are mounted around the structural core, and affixed to one another and on said structural core. 
     
     
       10. The blade claimed in claim 9, wherein said two laminated and complementary parts of said aerodynamic conformation covering comprise an upper surface part and a lower surface part, each of said parts comprising the upper and lower surface parts of the external shell and of the filling and conformation layer and being affixed to one another at a location of a leading edge and a trailing edge of said blade. 
     
     
       11. The blade claimed in claim 1 or 2, wherein said structural core has a transverse cross-section, along a chord of said blade, having a contour substantially parallel to the profile of said external shell of the aerodynamic conformation covering of which the filling and conformation layer is a sheet to compensate for differences in tolerance between said contour and said profile. 
     
     
       12. The blade claimed in claim 1 or 2, wherein the structural core has a transverse cross-section, along a chord of said blade, having a faceted contour based on simple geometric shapes, the filling and conformation layer of the aerodynamic conformation covering constituting a cushion to compensate for differences in shape between said contour and the profile of said external shell of said covering. 
     
     
       13. The blade as claimed in claim 1 to 2, wherein said structural core comprises a composite central spar, transverse ends of which are formed into a solid unit, each by means of a composite sole, a first said sole being disposed against the interior of the upper surface part and a second said sole being disposed against the interior of the lower surface part of a stress-bearing, rigid shell of said structural core, said central spar extending along the span of the blade, substantially at the center of the chord of the latter, and delimiting, together with said stress-bearing, rigid shell and a leading-edge spar of the structural core, a leading-edge box filled with a front filling element of said core. 
     
     
       14. The blade claimed in claim 13, wherein said structural core comprises a rear filling element disposed within said stress-bearing, rigid shell, behind said central spar of said core. 
     
     
       15. The blade claimed in claim 14, wherein each filling element of said structural core is constructed of a material selected from a group consisting of cellular material, foam, and laminated honeycomb. 
     
     
       16. Blade made of composite materials for a rotor of a rotorcraft and having an aerodynamic profiled section, said blade comprising (a) a stress bearing core providing structural resistance of said blade against centrifugal forces, flapping and drag bending moments and torsional moments about a longitudinal axis of said blade, said core having a chordwise cross-section contained with spacing within said blade aerodynamic profiled section and comprising (i) at least one spar made of rovings of fibers having high mechanical resistance and agglomerated by a polymerized synthetic resin;   (ii) a stress-bearing rigid shell, participating in said structural resistance, and made of at least one layer of fabric of fibers having high mechanical resistance and agglomerated by a polymerized synthetic resin, said layer of fiber fabric surrounding said spar and being made integral with said spar; and   (iii) at least one filling element made of a lightweight synthetic material disposed within said stress-bearing rigid shell and made integral with said stress-bearing rigid shell and said spar; and     (c) an aerodynamic conformation covering, surrounding said stress-bearing core and comprising: (i) an external thin rigid shell, having a chordwise cross-section defining said blade aerodynamic profiled section; and   (ii) a filling and conformation layer made of a non-stress-bearing light flexible and deformable material which fills said spacing between said stress-bearing core and said external rigid shell and connects said stress-bearing rigid shell of said stress-bearing core to said external rigid shell of said aerodynamic conformation covering.     
     
     
       17. The blade claimed in claim 16, wherein said thin, rigid shell of said aerodynamic conformation covering is made of a layer of thermo plastic resin. 
     
     
       18. The blade claimed in claim 16, wherein said thermoplastic resin of said external shell is dyed in the mass. 
     
     
       19. The blade claimed in claim 16, wherein said thermoplastic resin of said external shell is painted. 
     
     
       20. The blade claimed in claim 16, wherein said thermoplastic resin of said external shell is reinforced with fibers selected from a group consisting of inorganic and organic fibers. 
     
     
       21. The blade claimed in claim 16, wherein said thin, rigid external shell of said aerodynamic conformation covering comprises at least one anti-erosion layer made of fabric of fibers selected from a group consisting of organic and organic fibers which are agglomerated by a polymerical synthetic resin. 
     
     
       22. The blade claimed in claim 16, wherein said filling and conformation layer is made of a material selected from a group consisting of cellular material and flexible foam. 
     
     
       23. The blade claimed in claim 16, wherein said aerodynamic conformation covering consists of two laminated and complementary parts, which are mounted around the structural core, and affixed to one another and on said structural core. 
     
     
       24. The blade claimed in claim 16, wherein said two laminated and complementary parts of said aerodynamic conformation covering comprise an upper surface part and a lower surface part, each of said parts comprising the upper and lower surface parts of the external shell and of the filling and conformation layer and being affixed to one another at a location of a leading edge and a trailing edge of said blade. 
     
     
       25. The blade claimed in claim 16, wherein said structural core has a transverse cross-section, along a chord of said blade, having a contour substantially parallel to the profile of said external shell of the aerodynamic conformation covering of which the filling and conformation layer is a sheet to compensate for differences in tolerance between said contour and said profile. 
     
     
       26. The blade claimed in claim 16, wherein the structural core has a transverse cross-section, along a chord of said blade, having a faceted contour based on simple geometric shapes, the filling and conformation layer of the aerodynamic conformation covering constituting a cushion to compensate for differences in shape between said contour and the profile of said external shell of said covering. 
     
     
       27. The blade as claimed in claim 16, wherein said structural core comprises a composite central spar, transverse ends of which are formed into a solid unit, each by means of a composite sole, a first said sole being disposed gains the interior of the upper surface part and a second said sole being disposed against the interior of the lower surface part of a stress-bearing, rigid shell of said structural core, said central spar extending along the span of the blade, substantially at the center of the chord of the latter, and delimiting, together with said stress-bearing, rigid shell and a leading-edge spar of the structural core, a leading-edge box filled with a front filling element of said core. 
     
     
       28. The blade claimed in claim 16, wherein said structural core comprises a rear filling element disposed within said stress-bearing, rigid shell, behind said central spar of said core. 
     
     
       29. The blade claimed in claim 16, wherein each filling element of said structural core is constructed of a material selected from a group consisting of cellular material, foam, and laminated honeycomb. 
     
     
       30. Blade made of composite materials for a rotor of a rotorcraft and having an aerodynamic profiled section, said blade comprising (a) a stress bearing core providing structural resistance of said blade against centrifugal forces, flapping and drag bending moments and torsional moments about a longitudinal axis of said blade, said core having a chordwise cross-section contained with spacing within said blade aerodynamic profiled section and comprising (i) at least one spar made of rovings of fibers having high mechanical resistance and agglomerated by a polymerized synthetic resin;   (ii) a stress-bearing rigid shell, participating in said structural resistance, and made of at least one layer of fabric of fibers having high mechanical resistance and agglomerated by a polymerized synthetic resin, said layer of fiber fabric surrounding said spar and being made integral with said spar; and   (iii) at least one filling element made of a lightweight synthetic material disposed within said stress-bearing rigid shell and made integral with said stress-bearing rigid shell and said spar; and     (c) an aerodynamic conformation covering, surrounding said stress-bearing core and comprising: (i) an external thin rigid shell, having a chordwise cross-section defining said blade aerodynamic profiled section; and   (ii) a filling and conformation layer made of a non-stress-bearing light flexible and deformable material which fills said spacing between said stress-bearing core and said external rigid shell and connects said stress-bearing rigid shell of said stress-bearing core to said external rigid shell of said aerodynamic conformation covering.     
     
     
       31. A process for manufacturing a blade made of composite materials and having an aerodynamic profiled cross section, said process comprising the steps of (a) constructing a structural core in the shape of a primary structure including all structural elements of said blade; and   (b) surrounding said structural core with an aerodynamic conformation covering with the aid of a layer of a light and flexible, non-stress-bearing conformable material, and with a rigid and thin external shell which is profiled to a final aerodynamic profile of said blade.   
     
     
       32. The process claimed in claim 29, comprising surrounding said structural core with said aerodynamic conformation covering by mounting, around said structural core, two complementary laminated parts forming covering sand each one of which comprises a part of said layer of conformable material and a part of said profiled external shell, said two laminated and complementary parts being affixed against one another and said structural core. 
     
     
       33. The process claimed in claim 30, wherein each one of said two complementary laminated parts is made by calendaring or thermoforming a corresponding part of said profiled external shell constructed of thermoplastic resin, and by affixing a part of said filling and conformation layer on an internal face of said corresponding part of said external shell.